Electronic Spectroscopy of [FePAH]+ Complexes in the Region of the Diffuse Interstellar Bands: Multireference Wave Function Studies on [FeC6H6]+

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• 作者：Mathieu Lanza ; Aude Simon ; Nadia Ben Amor
• 刊名：Journal of Physical Chemistry A
• 出版年：2015
• 出版时间：June 11, 2015
• 年：2015
• 卷：119
• 期：23
• 页码：6123-6130
• 全文大小：300K
• ISSN：1520-5215

文摘

The low-energy states and electronic spectrum in the near-infrared鈥搗isible region of [FeC₆H₆]⁺ are studied by theoretical approaches. An exhaustive exploration of the potential energy surface of [FeC₆H₆]⁺ is performed using the density functional theory method. The ground state is found to be a ⁴A₁ state. The structures of the lowest energy states (⁴A₂ and ⁴A₁) are used to perform multireference wave function calculations by means of the multistate complete active space with perturbation at the second order method. Contrary to the density functional theory results (⁴A₁ ground state), multireference perturbative calculations show that the ⁴A₂ state is the ground state. The vertical electronic spectrum is computed and compared with the astronomical diffuse interstellar bands, a set of near-infrared-visible bands detected on the extinction curve in our and other galaxies. Many transitions are found in this domain, corresponding to d 鈫?d, d 鈫?4s, or d 鈫?蟺* excitations, but few are allowed and, if they are, their oscillation strengths are small. Even though some band positions could match some of the observed bands, the relative intensities do not fit, making the contribution of the [Fe鈥揅₆H₆]⁺ complexes to the diffuse interstellar bands questionable. This work, however, lays the foundation for the studies of polycyclic aromatic hydrocarbons (PAHs) complexed to Fe cations that are more likely to possess d 鈫?蟺* and 蟺 鈫?蟺* transitions in the diffuse interstellar bands domain. PAH ligands indeed possess a larger number of 蟺 and 蟺* orbitals, respectively, higher and lower in energy than those of C₆H₆, which are expected to lead to lower energy d 鈫?蟺* and 蟺 鈫?蟺* transitions in [FePAH]⁺ than in [FeC₆H₆]⁺ complexes.